Method of preventing offset



Patented Apr. 19, 1938 v UNITED V-(STATIIESV PATE- NT OFFICE METHOD or PREVENTl NG OFFSET Bruce A. Young, Chicago, 111., assignor to R. R.

Donnelley it Sons 00.,

, tion of Illinois No Drawing.

Chicago, 111., a corpora- Application December 9, 1935, Serial No. 53,675

6, Claims. (01.101-420) is cornstarch and the liquid is water which My" invention relates to the preventing'of the offsetting of ink from freshly printed sheets or webs, as for example of paper, during operations which immediately follow the printing, such as folding or winding in rollsin the case of webs,

or piling in the case of sheets.

The oifsetting of freshly printed ink onto whatever the printed sheets or webs may come into contact has always been a source of trouble in printing, particularly in the production of better I grades of printed work. As for example, the

ink may be offset onto parts of the, press, such as the rollers, folding mechanism, etc., thereof,

and is then transferred 'to the sheets or webs;

the objections resulting from methodshitherto proposed.

In accordance with my novel method I apply to the printed face of the freshly printed sheet a mixture of a neutral liquid and material in powdered form and of such characterthat at least the greater part thereof is insoluble in the liquid and maybe maintainedin a suspended.

condition in the liquid as for example by stirring it with stirring means inthe supplyjtank.

The liquid mayrbe of any suitable kind, asfor example, water or oil. Likewise, any suitable powdered material may be used, such, as for example, powdered talc, powdered mica, powdered magnesia, powdered aluminium hydrate, or starch, particularly corn starch as commonly provided, corn starch having been found, in practice to be very desirable for this purpose.

The liquid and powdered material may be used in any suitable proportions, the proportion of the powdered material to the liquid, by weight, being preferably about 2% to about 17% of the powdered materialto about 83% to about 98% of the liquid depending-on the speed at which the presses operate, the kind of paper used and the time which elapses between the printing and the stacking or folding of the sheets or'web. When, by way of example, the powdered material used should be unheated, as for example at about the temperature of ordinary cold service water, and

the mixture is to be used on highly calendered psheets printed on a cylinder fiat bed press and which thus move slowly past the means which spray the offset-preventing mixture to the sheets, about 2% of corn starch will preferably beused; where the mixture is to be used on sheets which move faster, as in the case of sheet rotary presses; about 3 of corn starch will be preferred; and where the mixture is to be used on webs printed on web-presses, the webs being of comparatively rough paper as for example news print, and the presses operating to drive the paper web at high speeds and fold the web almost immediately after printing, from about 11% to about 17% of corn starch, depending on the speed of the press, preferably is used.

'The mixture of liquid and powdered material may be applied to theprinted faces of the sheets orwebs against thefreshly applied ink, in any .suitable way, such as for example. by spraying it thereon as by means of spraying mechanism positioned to direct the spray against the sheet or web as the latter feeds through the press, or by roller means to which the mixture is supplied I and'contaoting the sheet or web. Where the mixture is to besprayed any suit-' able spraying means may be used. As for example, a liquid atomizing device, in which case it is preferred that the atomizing nozzle be of such constructionthat practically all of the liquid is atomized before it reaches the printed surface. As will be understood, the application to the freshly printed surface of the mixture referred tocauses the solid particles of material of the mixture to bedistributed over the surface which thus serve to mechanically separate the surface to which it is applied from a sheet or web fiatwise positioned against such coated surface, it

, having been found in practice that a relatively small amount of powdered material properly distributed over the surface, as above provided forf and which, when theliquid is evaporated or has been absorbed by the sheets: or webs does not present any perceptible excess to cause trouble in subsequent handling of thesheets or webs, will effectually prevent offset.

I Sincethe solid material, uponjthea evaporation or absorption of the neutral liqul ,by the sheet or web, ret s to its original form of'dry pow der, it does 11 t form dense or hard coatings on surfaces ont which;it may ran; When it falls on printing ollers for ink fountains it mingles with the ink and in fact is of the same nature as materials frequently incorporated in the ink itself when made. When it falls on moving parts of the press it does not tend to accumulate in objectionable dense masses, and may be easily dislodged.

It is furthermore desirable to obtain the best results that the powdered material used be of such character, as for example, as in the case of the various solid materials above mentioned, that they will not become softened by heat and will withstand considerable pressure applied against them as when the printed sheets are piled up to a height of several feet.

The liquid of the mixture serves to control the application of the powder to substantially evenly distribute it over the surface in a way not possible if the powder were dry. Furthermore, the liquid has an immediate, though temporary, effect in preventing offset. The particles of powder adhere to the inked surface and serve to hold a film of liquid over the ink at the time the latter is most easily offset, viz., immediately after printing.

What I claim as new, and desire to secure by Letters Patent, is:

1. The method of preventing the offsetting of ink from a freshly printed surface, comprising applying in a mist form to such surface a mixture consisting substantially entirely of a liquid and powdered material at least the greater portion of which is insoluble in the liquid.

2. The process which consists in applying to a freshly printed surface a mixture of a fugitive liquid and a powdered material, at least the greater portion of which is insoluble in the liquid.

3. The process which consists in applying to a freshly printed surface an essentially aqueous fugitive liquid and powdered starch, at least the greater portion of which is insoluble in the liquid.

4. The method as set forth in claim 3 in which the starch is corn starch and it comprises from 2 to 17% of the liquid.

5. The process which consists in applying to a freshly printed surface an essentially aqueous fugitive liquid and powdered material, at least the greater portion of which is insoluble in the liquid.

6. The method as set forth in claim 2, in which the moisture is applied in a mist.

BRUCE A. YOUNG. 

